Just to clarify, The "traffic in sight" reported was on the Tower frequency, and referring to a "circling aircraft", N64030 had already left the area to "go up the coast a bit". A short while later it was making a return trip Eastbound along the top of the mountains when the collision occurred, according to the radar track. The wreckage was in the mountains well north and outside of SMO towers airspace.
I added the Practice area frequency at the end of this recording, in the minutes after SMO is done with them. It is 122.775 from another one of my live feeds, it's usage is north of the SMO class Delta. It is a CTAF, and the controller is not on this frequency. It has the aircraft involved with instructors on board, (N4677V), the other aircraft is not heard on this frequency. My scanner did not pick up advisories from the other aircraft. "Semi Traffic and Malibu Traffic" is what you hear at the end of the recording, as many pilots use this verbage when using the frequency in this part of the practice area.
These accidents are rare, but the standard rule for pilots flying VFR is "see and avoid". A very sad day, will wait for the official report.